1. Field of Invention
This invention relates to microprocessor-based systems and particularly to battery backup of erasable memory in microprocessor-based systems.
In many microcomputer-based products, such as microprocessor-based photocopy sysems, there is a need to save pertinent volatile data during periods when the main power source to the system is interrupted. Such data may include indicators controlling use of the machine, counters, flags, check data, and information about work in process. Such data are generally stored in volatile random access memory, as opposed to nonvolatile read only memory.
2. Description of the Prior Art
Various techniques and methods have been employed for preserving volatile data in computer systems. The typical system is an uninterruptible power supply with sophisticated circuitry for sensing irregularities in the AC power source. Such systems are normally intended to enable continuous operation even upon interruption of power. Uninterruptible power supplies are generally expensive and not suited to microprocessor-based systems, particularly because the sophistication and expense of generally available uninterruptible power supplies may exceed that of the systems intended to be supported. What is therefore needed is a simple yet effective technique and apparatus for preventing loss of important information in systems where operation is permitted to be interrupted.